Sandwiched structural surfaces



Aug 30, 1966 E. B. DANE, JR 3,268fim Y SANDWICHED STRUCTURAL sunmcms Filed se t'. 4., 1964 4 Sheets-Sheet l INVENTOA ERNEST B. DANE, JR.

ATTORNEY Amgg 3% W66 E. E3. DANE, JR

SANDWICI'XED STRUCTURAL SURFACES 4 Sheets-Sheet 2.

Filed Sept. 4, 3.964

lNVENTO/P ERNEST B. DANE,JR.

I 1 ATTORNEY M Um 3 I 3 I I a q i A Aug. 30, 1966 E B. DANE, JR 3,253,924

SANDWICHED STRUCTURAL SURFACES Filed Sept. 4, 1964 4 Sheets-Sheet 3 ERNEST B. DANE, JR.

ATTORNEY Aug. 30, 1966 E. B. DANE, JR 3,263,924

SANDWICHED STRUCTURAL SURFACES Filed Sept. 4, 1964 4 Sheets-Sheet 4 ERNEST B. DANE, JR.

/ ATTORNEY United States Patent 3,268,924 SANDWICHED STRUCTURAL SURFACES Ernest B. Dane, Jr., 57 Tyler Road, Belmont, Mass. Filed Sept. 4, 1964, Ser. No. 394,419 7 tClaims. (till. 96)

This invention relates generally to structural surfaces and particularly to a variant sandwiched structure and a construction method useful in making vehicles, especially boats having doubly curved surfaces.

Ideal surface structures, more commonly called skins, for general applications are characteristically hard and strong. Skins applied to vehicles, such as boats, low speed private air-craft, specialized auto-bodies and corresponding models and prototypes are also desirably light. Skins are of single or sandwiched construction. Many single skins are made of a solid layer of metal or wood. Solid metallic skins, however, are noisy and have a relatively high weight-to-strength ratio. Wood, though light, is structurally weak, soft and is subject to shrinking and swelling. Recently, fiberglass, which overcomessome of the inherent limitations of wood and metal, has become popular. But fiberglass construction is expensive and has cogent anisotropic strength characteristics. Single skinned surfaces have certain other limitations and these will become apparent from the following description of some of the more common ones.

The typical wooden boat hull is representative of planked single skinned surfaces. Fabrication is on an inverted mold composed of cheap wooden frames and ribbands. The frames are serially spaced transversing the mold and widely spaced ribbands cross the frames and extend along the length of the mold. With no necessity for lightness, strength, or water tightness the mold is coarse, simple, and inexpensive. In building the hull, an initial layer of ribs are steam bent around the ribbands. Subsequently, longitudinal planks are laid over and secured to the ribs. Although involving simple molds, it is evident that boat bulls and other planked surfaces formed by this method are characteristically weak to bending and thus require extra thickness and are heavy. Moreover, the planks require careful fitting to insure water proofing at the joints when composed of wood and also require caulking to compensate for the swelling normally following changes in humidity.

To avoid deficiencies of planked surfaces, other methods for forming continuous single skins have been devised. For example, one method superimposes a series of water-proofed burlap sheets impregnated with plastic over an exactly shaped expensive mold. Though burlap can be easily worked, it often doesnt provide a sufficiently hard and strong surface. Stamped aluminum skins have also been used for vehicular surfaces. Still, a stamped aluminum body requires an expensive mold and is particularly noisy in boating applications.

On the other hand, sandwiched skins offer many advantages over single skins. A sandwiched skin may be generically defined as a structure composed of high-density material, such as metal or fiberglass, bonded to an inexpensive core of relatively thick low-density material. The function of the core is to mechanically stabilize the thin surface faces and to prevent shear between them. Thus, sandwiched construction puts the strong material in the outside surfaces and the light comparatively weak core, such as foam or honeycomb, on the inside where there is substantially less loading. Sandwiched construction features a stiff and strong structure having a low weight-to-stiffness and strength ratio with good damping characteristics which eliminates noise. Numerous embodiments and methods have been proposed for fabricating sandwiched skins. These, however, generally prove Patented August 30, 1966 costly especially where compound curves or shapes are attempted.

For example, one sandwiched structure: proposed for doubly curved surfaces comprises a continuous cellular core bounded by skin layers consisting of metallic strips adhesively secured in over lapping or shingled relation to one another. Since the core is continuous, the mold, upon which it is fitted prior to the laying of the skins, must have exacting contours if the concave surface is to assume the desired shape. This structure would be appropriate where a concave surface must comply with precise design specifications, such as in the design of high resolution radar reflectors. However, because of the neoessity of an elaborate mold, it doesnt offer the most economical approach in applications where reduced surface accuracy is acceptable.

With aim towards avoiding elaborate molds, a reinforced fiber glass sandwiched structure using hollow interlocking panels as a core has been introduced. This construction begins with the laying of a plurality of rectangular shaped hollow panels against a simple wooden frame. The panels are composed of extruded fiberglass and are shaped on the sides to permit hinging of adjacent panels. To smooth the core surface, grooves between panels are later covered with filler. Inner and outer skins composed of one or more layers of fiber-glass cloth reinforced plastic are then secured to the core. It should be pointed out, that although the need for a well defined mold is alleviated, the individual panels are composed of expensive fiber glass material and must be appropriately shaped on the sides to allow socketing. As the rectangular panels form a substantially continuous core this approach is not Well suited for the construction of compoundly curved surfaces. Because of the anisotropic properties of the fiberglass planks, the present structure also compromises surface strength. Moreover, as a substantial amount of dense fiberglass is used in the core and especially around the socket shaped sides, it has the added disadvantage of being heavy.

Various techniques are available for constructing other kinds of sandwiched skins, such as those using contacting solid rectangular wooden planks in their cores. Wooden cores, however, are susceptible to shrinking and swelling. Requiring careful fitting they are also expensive to manufacture. Other cores formed by injecting expandable resinous materials between preformed panels recently have gained wide attention. But these are only suited for mass production due to the extremely costly dies required in preforming the panels. Furthermore, as the resinous material is homogeneous extra strength core material cannot be distributed to areas where needed.

In view of the aforementioned limitations of general structural surfaces used in vehicles and particularly those in boats, and the shortcomings of corresponding construction methods, applicant has as the broad object of his invention to provide an improved means and method for making doubly curved surfaces.

Another object of his invention is to provide an improved means and method for constructing a stiff, strong, light and low noise structural surface particularly suited for vehicles.

Another object of his invention is to provide an improved method for fabricating a surface skin on a coarse and inexpensive mold.

A specific object of his invention is to provide an improved method for constructing a doubly curved structure on an inexpensive mold and having a light, insulating core with strong and stiff surfaces.

Another specific object of his invention is to provide an improved method and means for fabricating a boat hull having favorable bouyant characteristics.

Another specific object of his invention is to provide an improved method and means for making a boat that is essentially noiseless.

Another specific object of his invention is to provide an improved method for building a boat having rigid internal structural supporting members.

' It is another object of the invention to provide a method for constructing boats with compound surfaces at a moderate cost.

These and other objects are met by a variant sandwiched structure composed of individually shaped foam plastic blocks bounded by inner and outer skins made of thin metallic strips. In accordance with the method of construction, a substantially continuous layer of foam plastic blocks is lightly tacked to a coarse inverted mold of the kind used in planked wooden boat construction. Higher density blocks are applied to areas where special strength is needed. Once in place, the outside faces of the blocks are rasped or sanded to the desired curvature. Next the external skin is fabricated by bonding one or more layers of overlapping thin metallic strips to the shaped blocks, heavier strips similarly applied to areas of special strength. Each strip is thin enough to easily follow the definition of the blocks, and narrow enough to avoid a compound curvature within any one strip. Skins are fabricated one layer at a time, each layer being bonded to the preceding one by a non-shrinking cement. Upon completion of the external skin, the entire structure is turned upright and the mold removed. Next, the internal skin, likewise, fabricated of overlapping metal strips, is built one layer at a time to the desired thickness. Structurally supporting members, such as the bulkheads, webs and transoms in boats, are rigidly fastened to both inner and outer skins. Preferably, they are built into the original mold and bonded to the outer skin as it is laid. When the mold is removed these members remain with the skin. The resulting sandwiched structural surface features a low weight-to-strength ratio, a high strength and stiffness factor, and is virtually noiseless. The method allows the construction of doubly curved structural surfaces on coarsely defined molds at moderate cost and is particularly useful in boat construction. These and other features of the present invention will be apparent from the following detailed description taken in conjunction with the following drawings of which:

FIG. 1 illustrates the mold and core block arrangement used to initiate construction of a spherically curved sandwiched structure,

FIG. 1A is a cross sectional view of a completed spherically curved structure built in accordance with the invention,

FIG. 1C is a detailed illustration of a portion of the structure of FIG. 1A,

FIG. 1B is a top view of the structure of FIG. 1C,

FIG. 1D is a bottom view of the structure of FIG. 1C,

FIG. 2 illustrates the construction of a typical boat hull in accordance with the invention,

FIG. 2A is a detailed view of the stern section of the hull of FIG. 2, and

FIG. 2B illustrates the interface between structurally supporting members and the skins for the hull of FIG.2.

FIGS. 1, 1A, 1B, 1C and 1D illustrate the broad concept of the invention embodied in a spherically curved surface. As illustrated in FIG. 1 a number of blocks 20 are lightly tacked on a coarse inverted mold of the kind used in Wooden boat construction; that is, a mold made of a series of transverse sawn wood frames 8 connected by laterally spaced longitudinal ribbands 14. Blocks 20, which bridge the gaps in the mold, are composed of light and relatively rigid material that can be easily be worked by rasping, filling, or sanding. Foam plastic or honeycomb are preferred core materials because they have good mechanical characteristics and cut easier than the proverbial cheese. Blocks 20 are initially oversized to allow shaping, but otherwise need not be of any particular configuration. However, wedge shaped ones are helpful in sharply curved area. Pins, staples, tape, contact cement, double headed concrete nails or the like may be used for tacking, as the only requirement is the ability to separate the mold and the blocks upon roll-over.

When all in place, blocks 20 are filed, sanded, or rasped until the outline of the blocks takes on the desired shape. Upon being cleaned of plastic dust they are ready to receive the outer skin. The outer skin consists of one or more layers of very thin metallic strips, the strips in each layer in overlapping relation with one another and forming a continuous and quite smooth surface. More specifically, FIGS. 1B and 1C show details in the construction of a three layer outer skin. The first layer is formed of strips 521;, 54a, the second layer of strips 52b, 54b, 56b and the final strips 520, 54c, and 560. To accentuate features of construction, the thickness of the metal sheets in each strip is greatly exaggerated and individual sheets are shorter than they would be on an actual surface. Successive sheets of each strip are overlapped and permanently bonded at the ends 33 and edges. It is essential to the fabrication of a strong skin that proper regard be given in overlapping the edges of all adjacent strips; for instance, the overlap 33' between the formost edge of strip 540 and the back edge of strip 520 or the overlap 33" between strips 54c and 56c etc. The amount of overlapping in the edges should be aimed at equalizing the shear strength of the cement with the tensile strength of the metal so the strength of edge joints is substantially constant in any direction. As a guide a well cemented lap of has a shear strength essentially equal to the tensile strength of the more common low cost metals of .006" thickness. Alternately, the strips may be overlapped to the extent of one-half of their width whereby each layer forms a uniform outer surface by itself. This alternate arrangement has the added advantage that the register of successive layers is less critical.

Each sheet is thin enough to easily follow the block faces and sufficiently narrow to avoid a compound curve within any one sheet. Except for high strength areas, a thickness .006 usually proves convenient. A width of 6" is suitable for flat areas, whereas, proportionately narrower sheets are applicable where the curvature is comparatively sharp. Lengthwise, sheets either extend clear across the structure or are as long as the curve permits. Styron, or non-shrinking catalyst polymerizing cements such as the epoxies, or other cements that similarly do not depend on solvent evaporation, serve as suitable cementing agents.

To enhance surface smoothness, skin layers are fabricated one at a time. Consequently, once strip 52a is formed, adjoining strips 54a, 56a, etc., in the first layer are subsequently bonded to the blocks, the successive sheets in each strip having overlapping ends. The work progresses along the longitudinal axis of the mold until the first layer skin is complete. Next the second layer skin is built beginning with strips 52b, 54b, 56b, etc., these strips being cemented to underlying strips of the first layer. Again, the work progresses down the mold until the second layer is completely installed. Work then extends to the third layer starting with strips 520, 54c, 560.

After the outer skin is completed the entire structure is rolled upright, the mold removed, and the inner skin constructed in the same Way. Illustrated in FIGS. 1C and 1D, first inner layer skin, beginning with strips 62a, 64a and 6611, are cemented to the inner faces of the blocks with similar lap jointing of successive ends and edges. Subsequently, second and third layers of inner skin, initiated by strips 62!), 64b, 66b and 620, 64c, 66c respectively, are applied one layer at a time. When fabrication is complete, the structural surface appears as shown in FIG. 1A.

Skins may be laid by machine or, where only a few surfaces are to be built, more simply by hand. Where a machine is used applicant suggests it carry the coil of stock, and spray or spread cement, and have roller to press the strip down tight. The spray may either mix the epoxy its catalyst and hardener outside the nozzle, or may use a solution already mixed and carried in a tank. Additionally, it may need a finger to trace the edge of the preceding strip and to guide shearing rolls that will trim the edge of the next strip to be fit, if such trimming proves necessary. Other suggested implements would include a revolving wire brush to better clean the surfaces of the strips, and a cleaning tank witharticulation to allow the tank to remain upright while the main unit follows curves in the hull. The machine should be mounted on wheels for maneuverability and should be supported by an overhead crane with a counterweight to relieve the operators load.

BOAT CONSTRUCTION Construction of mold The above described method may be specifically applied to the construction of boats. Consistent with the invention, four sections of a boat hull are shown in FIG. 2 in differing stages of development. Construction begins with the fabrication of an inexpensive inverted mold composed of sawed wooden frames 8, serially disposed along and transversing the longitudinal axis of the hull. The frames are interconnected by ribbands 14 that terminate at the stern and stern sections of the mold. structurally supporting members 12, such as floor supporting webs or bulkheads, are of non-swelling material and a poor conductor of heat, such as pregwood or marine grade wood. Preferably, they are built into the original mold. A first series of joined pairs of metallic unequal legged angles 9 are installed along the periphery of such members to serve as an interface between each member and outer skin. The longer and protruding leg has a flat section that receives the initial layer of the outer skin. A second series of angle pairs 13 are installed just inside the periphery for connection with the inner skin. As shown in FIG. 2B, the gap between opposing pairs of angles 13 and 9 is just enough to allow fitting of a foam plastic block between flats, and to allow the top of the flats to lie flush with the remainder of the block. Angle pairs are mutually connected to the member by bolt 15.

Illustrated in FIGS. 2 and 2A, arcuate heavy central plate 75 built into the mold, supports the stem section of the hull. A series of forward and back edge angles 73 and 77, respectively, are disposed on each side along the length of the plate. The flats of the forward channel form a V-shaped angle with each side of the plate and the flats of rear angles form an obtuse angle with each side thereof. The angles are light enough to enable handworking of the flats to the proper bevel. Alternately, tabs could be cut into the two edges of the plate and then stretched to form the angular section. In either event, there is enough protruding flat area in the forward and rear edges of plate 75 to support the initial layers of the inner and outer skins.

Fitting of blocks When the .mold is completed, foam plastic blocks 20 are lightly tacked to the ribbands in the manner previously described in connection with FIG. 1. Blocks around supporting members are shaped and snugly fitted between the flats of opposing angles. FIG. 2B specifically shows how the blocks are fitted between the flats of angles of support member 12. FIG. 2A illustrates how blocks 20 are fitted between the flats of the angles in the stem. After blocks around the stem, bulkheads and floor supporting webs are in place, blocks are tacked to the ribbands covering the remaining portions of the hull as shown in section 0 of FIG. 2. Higher density blocks 20a are used in areas requiring increased strength. For example, extra core strength is needed at the rail in order that the deck can be rigidly secured along the periphery.

Accordingly, a rim of higher density block 20a is fastened to the mold at deck level. Also, additional strength is required all along the keel, under-chain plates and at any openings in the hull. Solid wood could be used, but a more workable core for these areas is a block of dense foam plastic. After tacking, the outer faces of all blocks are rasped until the combined contour assumes the shape desired of the hull. When raspin-g is completed some sanding may be required to level the edges of the blocks and to otherwise develop an even surface for receiving metal strips. The surface should be cleaned perhaps with a vacuum cleaner, to remove block dust and any other foreign matter that would weaken the bond with the outer skin.

Outer skin Long metallic strips .006" thick and 6 wide are next laid across the blocks. They may be laid longitudinally, or transversely as shown in Section D of FIG. 2. It is expected that strips covering some of the more curved sections, such as the stem sections, will have to be tapered to permit a uniform fit. Ends and edges of successive strips are overlapped in accordance with FIG. 1C.

Laying of the skins preferably begins near the center of the hull where side and bottom are most nearly parallel with the center line. Lay up then proceeds towards the stem and stern sections in either order, the individual metal strips extending from port to starboard. FIG. 2A shows how foremost strips 32a, 34a, 36a, which must be tapered to smoothly follow the curve, are cemented to the flats of angles 73 and. to blocks 26 in the .stem section. FIG. 2 shows final strips 540, 56c, and 58c of the third of three layers a, b, c of the exterior skin applied to the stern. While laying the skin a press roller should be employed to force each strip down on the cement and simultaneously drive out any air bubbles. After the first layer skin is finished the small step lbetween abutting edges of successive strips may have to be filled with epoxy to smooth the sunface. The first layer completed, the second layer is next laid, construction again starting at the point of maximum \beam. This layer extends from port to stanboard and otherwise conforms with FIGS. 1B and 1C. Likewise, the strips in the second layer are pressed to improve bonding and epoxy filler possibly used to smooth the final surface. The layers are thusly fabricated one at a time until the outer skin attains the necessary thickness.

Except for areas requiring extra strength, metallic sheets having a thickness of .006 should provide ample tensile strength. In areas where the skin must be stronger, for instance along the rail, around. the keel and chain plates, thicker sheets are used. These may be integrated into the skin and without causing bulge in the s-unface by initially sanding or cutting a suflicient depression into the supporting dense core blocks 20a to offset the combined additional thickness of the sheets.

Inner skin When laying of the outer skin is concluded the entire structure is rolled over and the mold removed. If structurally supporting members were originally built into the mold they will hold their shape well enough, and subsequently frames and ribbands are easily removed. Starting again near the center section, the inner skin is identically laid. As shown in FIG. 2A, at the stem first strips 42a, 44a, 46a of the initial inner layer are cemented to inner angles 77 and blocks 2t As construction goes on, the first layer becomes continuous being internupted only around bulkhead and web members. There strips of the initial layer are mutually joined to the flats of angles 13 and the adjacent blocks snugly fitted around the protruding member. The inner skin is built from port to stanboard one layer at a time and a roller employed to improve the cement bond.

Transom The transom may be fabricated of the same kind of sandwiched section having a number of fitted foam plastic blocks between inner and outer metallic skins. Broader and thicker strips can be used or even single sheets, as this section has simple curves. Strong filler is inserted around the edges where the inner skin of the transom joins the cross section of the aft portion of the hull. The filler increases the shear stiffness of the joint. Also, a few V-shaped strips mutually cemented to the corner-most strips of the inner skin of the hull and transom improves strength. Where the curvature is appreciable, short strips provide a more suitable fit. The junction is otherwise strengthened by angle sections distributed along the corner. The outer skin at the junction is developed by bending the corner strips and integrating the initial and additional layers into the corresponding skin layers of the transom and hull. In other words, this portion of the outer skin is fabricated along with the rest of the outer surface of the hull, except the corner-most strips are bent to fOllOlW and cover the junction.

Floor timbers Floor timbers to support ballast, keels, engine beds, etc., are formed as I or box beams with a lower flange composed of a heavier metal strap just inside the outer skin, a web of pregwood, fiberglass, plastic or metal, and an upper flange of a metal strap just below the cabin sole. Over the part of the bottom where floors are fitted, the curved skin is laid between them, and cemented to angles bolted to the webs; or if the design is not too deep, the space between floors can be filled with foam and the inner skin run over the top of the upper flanges. Some empty space should be left along the center line to catch [water that would otherwise be trapped above the cabin sole. This space must be then lined, and then must be accessible to pumping equipment.

Decks Decks are made of the same light sandwich construction as the sides, or less expensively, of marine grade plywood With fiberglass covering. At the edges, the peiriphery of the deck is screwed and cemented to one rim strip of dense plastic material. If the outer skin is composed of athwartship strips, they can be left long enough to lap over the deck and cemented under a cowering board. A triangular section strip of extra foam might be fitted inside the dense strip at the rail, so that the inner skin could swing inboard to form a diagonal brace before being cemented to the under side of the deck. This foam must be added after removal of the mold but before the inner skin is in place.

Chain plates need cover considerable area of both inner and outer skin in order that the cement and bolts have a good hold. Four strips of SS on each skin of a thickness sufficient to give the required strength when brought out together at the top and fanned out over the inner skins below might do. The hole for the pin is drilled after assembly of the plate.

Suitable metal for boat skins The alloy Titanium 6A1 4Va is a first choice, for it is light (.161 #/cu. in. SP. GR. 4.43) strong (120000 psi. YS) and highly corrosion resistant. However, it may be much too expensive for such large structures. Alternatively, aluminum alloy 5083 H34 (.096 #/cu. in., 39000 psi YS) can be used for the inside plies. The same alloy Marten Hardcoated, can be used for outside plies, provided it can be economically purchased. If Marten Hardcoated alloy is too expensive, an outer layer \of 316 stainless steel, perhaps .002" thick would suffice. Well cemented to .040" to .060" of aluminum, it is quite resistant to tearing, ,Any tears that do occur need prompt attention, however, as the large difference in electrolyte potential causes rapid attack on the aluminum. The Titanium alloy would make a very good outermost layer. A fiber glass exterior also is possible. It would contribute very little to the strength, and could be heavier than the others, but probably gives the best protection against corrosion. Flake glass is another possibility as is ribbon glass, which might even be used in place of the metal strips for the entire skin.

While particular embodiments of the invention have been described it should, of course, be understood that it is not to be so limited. Modifications may be made and yet remain within the intended scope of the invention. For instance, in the construction of the boat structurally supporting members were described as being constructed into the mold. This need not be the case, as they may be added after removal of the mold. One alternate construction would be to apply wide blocks of wood or very dense core material during block lay up to areas that will underlie :structunally supporting members. Continuous inner and outer skins will then cover these blocks after the two skins have been applied. Upon removal of the mold structurally supporting members are inserted over the denser blocks and secured thereto by screw fastenings which protrude through the inner skin and into the blocks. It should be pointed out, moreover, that other or core material, metals, or even non-metallic isotropic sheet material, other than of the kind described, may be incorporated and still be within the spirit of the inven tion. Also, the core may take of long foam plastic planks arranged side by side, instead of blocks, and these may be beveled into shape by machine or hand when the contour of the structure is formed. Finally, although the metal strips have been shown in the drawings as transversing the longitudinal axis of the mold, they could be laid longitudinally or diagonally if these skin configurations prove more convenient.

Because of these and other possible modifications it is therefore comprehended, by the appended claims, to cover any such modifications falling within the true spirit and scope of the invention.

What is claimed is:

I claim:

ll. In a boat hull having a deck and further comprising;

(a) a plurality of foam plastic blocks disposed along said hull each having mutually opposed first and second faces, blocks of higher density material forming a rim in said hull along said deck level, and the periphery of said deck rigidly fastened to said rim of higher density blocks,

(b) a first metallic skin comprising at least one layer of overlapping metallic strips cemented to said first faces of said blocks,

(c) a second metallic skin comprising at least one layer of overlapping metallic strips cemented to a said second faces of said blocks, and

(d) at least one structurally supporting member fastened to said first and second skins and projecting perpendicularly from said second skin.

2. A boat hull having a deck and further comprising;

(a) at least one structurally supporting member having an arcuate base section, said member extending upward from the bottom of said hull, and also comprising,

(1) a first series of metallic angle pairs rigidly fastened along the periphery of said base section of said member, one fiat of each of said angles extending perpendicularly outward from said member,

(2) a second series of metallic angle pairs rigidly fastened to said member and inwardly displaced from said periphery of said base section of said member, one flat of each of said second series of said angles extending perpendicularly outward from said member,

(b) a plurality of foam plastic blocks each having mutually opposed first and second faces distributed along said hull, blocks of higher density material forming a rim in a plane substantially level with said deck, the periphery of said deck rigidly fastened to said rim of higher density blocks, and blocks in proximity with said supporting member snugly fitted between said flats of said first and second series of angle pairs,

() at least one outer skin layer of overlapping metal strips, said strips of said outer layer cemented to said first faces of said blocks and cemented to said flats of said first series of angles, and

(d) at least one inner skin layer of overlapping metal strips, said strips of said inner layer cemented to said second faces of said blocks and cemented to said flats of said second series of said angles.

3. A boat hull as defined in claim 1 further comprising,

(e) a stem comprising a central plate having a forward and back edge and further comprising,

(1) a third series of metallic angles disposed along said forward edge of said plate and on each side thereof, the flats of said first series of angles forming a V-shaped channel on each side of said forward edge of said plate,

(2) a fourth series of metallic angles disposed along said back edge of said plate and on each side thereof, the flats of said fourth series of angles forming an obtuse angle with said plate,

(3) foam plastic blocks along each side of said plate and in said V-shaped channel of said plate,

(4) strips of said first metallic skin cemented to said flats of said third series of angles and cemented to said blocks along said plate, and

(5) strips of said second metallic skin cemented to said flats of fourth series of angles.

4. A boat hull as defined in claim 2 further comprising,

(e) a stern comprising a central plate having a forward and back edge and further comprising,

( l) a third series of metallic angles disposed along said forward edge of said plate and on each side thereof, said first series of angles forming a V-shaped channel on each side of said forward edge of said plate,

(2) a fourth series of metallic angles disposed along said back edge of said plate and on each side thereof, the flats of said fourth series of angles forming an obtuse angle with said plate,

(3) foam plastic blocks along each side of said plate and in said V-shaped channel of said plate,

(4) strips of said first metallic skin cemented to said flats of said third series of angles and cemented to said blocks along said plate, and

10 (5) strips of said second metallic skin cemented to said flats of said fourth series of angles.

5. In a boat hull having a deck and further comprising:

(a) at least one structurally supporting member extending upward from the bottom of said hull,

(b) a plurality of foam plastic blocks each having mutually opposing first and second faces distributed along said hull, the periphery of said deck rigidly fastened to blocks in proximity therewith,

(c) at least one outer skin layer of overlapping metal strips, said outer skin layer secured to said first faces of said blocks and secured to said structurally supporting member, and

(d) at least one inner skin layer of overlapping metal strips, said inner skin layer secured to said second faces of said blocks, and secured to said structurally supporting member.

6. A boat hull as defined in claim 5 further comprising:

(e) a stern section, and

(f) means for securing said stern section respectively to said inner and outer skin layers.

7. In a boat hull having a deck and further comprising:

(a) a plurality of foam plastic blocks each having mutually opposing first and second faces distributed along said hull, the periphery of said deck rigidly fastened to blocks in proximity therewith,

(b) at least one outer skin layer of overlapping metal strips, said outer strip layer secured to first faces of said blocks,

(c) at least one inner skin layer of overlapping metal strips, said inner skin layer secured to said second faces of said blocks, and

(d) at least one structurally supporting member extending upward from said inner skin layer and secured to blocks underlying said member and under said inner skin layer.

References Cited by the Examiner UNITED STATES PATENTS 1,643,329 9/1927 Baribault 96 2,447,609 8/1948 Breece 156298 2,888,975 6/1959 Benedict 156-298 3,050,208 8/1962 Irvine 2209 3,093,847 6/1963 Strecker 96 3,174,166 3/1965 Ehrenberg et a1. 9-6

MILTON BUCHLER, Primary Examiner.

FERGUS s. MIDDLETON, Examiner.

D. P. NOON, A. H. FARRELL, Assistant Examiners. 

1. IN A BOAT HULL HAVING A DECK AND FURTHER COMPRISING; (A) A PLURALITY OF FOAM PLASTIC BLOCKS DISPOSED ALONG SAID HULL EACH HAVING MUTUALLY OPPOSED FIRST AND SECOND FACES, BLOCKS OF HIGHER DENSITY MATERIAL FORMING A RIM IN SAID HULL ALONG SAID DECK LEVEL, AND THE PERIPHERY OF SAID DECK RIGIDLY FASTENED TO SAID RIM OF HIGHER DENSITY BLOCKS, (B) A FIRST METALLIC SKIN COMPRISING AT LEAST ONE LAYER OF OVERLAPPING METALLIC STRIPS CEMENTED TO SAID FIRST FACES OF SAID BLOCKS, (C) A SECOND METALLIC SKIN COMPRISING AT LEAST ONE LAYER OF OVERLAPPING METALLIC STRIPS CEMENTED TO A SAID SECOND FACES OF SAID BLOCKS, AND (D) AT LEAST ONE STRUCTURALLY SUPPORTING MEMBER FASTENED TO SAID FIRST AND SECOND SKINS AND PROJECTING PERPENDICULARLY FROM SAID SECOND SKIN. 